R 17 date format exercise

> x=as.Date("1970-01-02")# Date format 
> x
[1] "1970-01-02"
> class(x)
[1] "Date"
> unclass(x)
[1] 1
> as.Date("2018/01/24")
[1] "2018-01-24"
> x=as.POSIXct("2020-01-24 10:30:00")# Convert to time format   Restore to the number of seconds 
> x1=as.POSIXlt("2020-01-24 10:30:00")# After restore, there is a large list 
> unclass(x)
[1] 1579833000
attr(,"tzone")
[1] ""
> unclass(x1)
$sec
[1] 0

$min
[1] 30

$hour
[1] 10

$mday
[1] 24

$mon
[1] 0

$year
[1] 120

$wday
[1] 5

$yday
[1] 23

$isdst
[1] 0

$zone
[1] "CST"

$gmtoff
[1] NA

> ?DateTimeClasses# View help documents 
> x1$yday+1# Draw days 
[1] 24
> weekdays(x)# Day of the week 
[1] " Friday "
> months(x)# Return months 
[1] " January "
> quarters(x)# Return to month 
[1] "Q1"
> Sys.Date()# Return system date 
[1] "2022-03-02"
> Sys.time()# Return to system time 
[1] "2022-03-02 10:13:40 CST"
> date=c("01 10, 2012 10:40","12 09, 2011 09:10")
> date
[1] "01 10, 2012 10:40" "12 09, 2011 09:10"
> x=as.POSIXct(date,format="%m %d, %Y %H:%M")# Returns the standard format 
> class(x)# Subclass  "POSIXct"  Parent class "POSIXt" 
[1] "POSIXct" "POSIXt" 
> t1=as.Date("2016-03-01")
> t2=as.Date("2016-02-28")
> t1-t2# Get the time difference 
Time difference of 2 days
> t3=as.POSIXct("2015-03-12 12:00:00")
> t4=Sys.time()
> class(t4)
[1] "POSIXct" "POSIXt" 
> t4-t3# Decimals are displayed 
Time difference of 2546.926 days
> t4-t2# Different formats cannot be divided 
[1] "2022-03-02 05:32:41 CST"
Warning message:
Incompatible methods ("-.POSIXt", "-.Date") for "-" 
> as.numeric(t4-t3)
[1] 2546.926
> difftime(t4,t3)#t4-t3,units="weeks"units Return unit 
Time difference of 2546.926 days
> difftime(t4,t3,units="mins")#t4-t3,units="weeks"units Return unit 
Time difference of 3667574 mins
> ?seq
> l=seq(t3,t4,"year")# A sequence of equal differences t3 To t4
> l=length(l)
> l
[1] 7
> seq(t3,by="-2 month",length.out=12)# Push forward twice , The length is 2
 [1] "2015-03-12 12:00:00 CST" "2015-01-12 12:00:00 CST" "2014-11-12 12:00:00 CST" "2014-09-12 12:00:00 CST" "2014-07-12 12:00:00 CST"
 [6] "2014-05-12 12:00:00 CST" "2014-03-12 12:00:00 CST" "2014-01-12 12:00:00 CST" "2013-11-12 12:00:00 CST" "2013-09-12 12:00:00 CST"
[11] "2013-07-12 12:00:00 CST" "2013-05-12 12:00:00 CST"
> 
> as.Date("2010/11/04")# Into time 
[1] "2010-11-04"
> as.Date("11-04/2010",format="%m-%d/%Y") # Convert to standard format    
[1] "2010-11-04"
> ts=Sys.Date()# system time 
> class(ts)
[1] "Date"
> weekdays(ts)# What day 
[1] " Wednesday "
> months(ts)
[1] " March "
> quarters(ts)# quarter 
[1] "Q1"
> as.POSIXct("11-04 2016,33:59 23h",format="%m-%d %Y,%M:%S %Hh")# A standard format 
[1] "2016-11-04 23:33:59 CST"
> t=strptime("11-04 2016,33m59s 23h",format="%m-%d %Y,%Mm%Ss %Hh")## Convert to standard format 
> l=as.POSIXct("1986-11-04 02:00:00")# Character to time 
> difftime(t,l,units="secs")# Phase difference length 
Time difference of 946848839 secs
> difftime(t,l,units="mins")
Time difference of 15780814 mins
> difftime(t,l,units = "hours")
Time difference of 263013.6 hours
> difftime(t,l,unit="days")         
Time difference of 10958.9 days
> length(seq(l,t,"month"))# Second difference 
[1] 361
> length(seq(l,t,"year"))
[1] 31
> seq(t,by="-1 month",length.out=12)# Push forward -1 Months , The length is 12
 [1] "2016-11-04 23:33:59 CST" "2016-10-04 23:33:59 CST" "2016-09-04 23:33:59 CST" "2016-08-04 23:33:59 CST" "2016-07-04 23:33:59 CST"
 [6] "2016-06-04 23:33:59 CST" "2016-05-04 23:33:59 CST" "2016-04-04 23:33:59 CST" "2016-03-04 23:33:59 CST" "2016-02-04 23:33:59 CST"
[11] "2016-01-04 23:33:59 CST" "2015-12-04 23:33:59 CST"